How to find center of a marker in an accurate way?

Question

I want to get the value of the center of the marker. as a picture below.

I have tried to calculate the center of the marker by calculating from the corner of the marker. So, I already got the center of the marker but it was not accurate values as I want. When the marker is not parallel to a camera, the calculated center has shifted from the center of the marker as a picture below.

I would appreciate if you could give me some suggestions to find the center of the marker in an accuracy way.

I would like to apologize if my question is not clear enough. Please let me know what I have to improve.

Answer 1

Since your image is at an angle, you can use a perspective transform to obtain a bird's eye view of the image. To obtain the center of the marker, you can first find the corners using the Shi-Tomasi Corner Detector or the Harris corner detector and then use geometry calculations based on the found corners to obtain your center point.